five

Like all chordates, vertebrates have a notochord, a dorsal, hollow nerve cord, pharyngeal slits, and a post-anal tail. What other characteristics do vertebrates have?

These five classes are fish, amphibians, reptiles, birds, and mammals. Fish (including sharks) make up the largest group of vertebrates.

Vertebrates can be subdivided into five major groups: fishes, amphibians, reptiles, birds, and mammals. Amphibians, reptiles, birds, and mammals are ranked as classes.

Humans, birds, mammals, reptiles, amphibians, and fish are all vertebrates. There are seven living classes of vertebrates.

As chordates, vertebrates have the same common features: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. Vertebrates are further differentiated from chordates by their vertebral column, which forms when their notochord develops into the column of bony vertebrae separated by discs.

The notochord is the defining structure of the chordates, and has essential roles in vertebrate development. It serves as a source of midline signals that pattern surrounding tissues and as a major skeletal element of the developing embryo.

The primary difference between the two is that vertebrates possess a backbone and an internal skeleton. In some vertebrates, the bones are replaced with cartilage, as seen in sharks. Another defining characteristic of vertebrates is that they reproduce sexually.

Although the vertebral column is perhaps the most obvious vertebrate feature, it was not present in the first vertebrates, which probably had only a notochord. The vertebrate has a distinct head, with a differentiated tubular brain and three pairs of sense organs (nasal, optic, and otic).

Like all of these animals, we are deuterostomes – meaning that during embryo development, our anus forms before our mouth. In other words, we are vertebrates, which are a form of chordate, which are themselves a form of deuterostome.

Sponges, corals, worms, insects, spiders and crabs are all sub-groups of the invertebrate group – they do not have a backbone. Fish, reptiles, birds, amphibians and mammals are different sub-groups of vertebrates – they all have internal skeletons and backbones.

Today, spines or quills are found in four major groups of living mammals: hedgehogs (Erinaceomorpha: Erinaceidae, Erinaceinae), tenrecs (Afrosoricida: Tenrecidae, Tenrecinae), echidnas (Monotremata: Tachyglossidae), and rodents (Rodentia).

Greenland shark